The present invention relates to a fuel injection system for an externally ignited internal combustion engine, and more particularly to such a system including fuel injection valves, and a fuel distributing unit with fuel metering valves which are jointly changeable for the purpose of varying their flow passage cross-section to regulate the quantity of fuel flowing to the fuel injection valves. The fuel metering process is effected with a constant pressure difference. Disposed in each fuel flow path downstream of the fuel metering valves is a valve, whose flow passage cross-section can be changed by means of a flexible member. The flexible member for each valve separates two chambers in the valve, with the pressure in the first chamber of each valve being the fuel pressure of the fuel downstream of its respective metering valve. At least one valve is in the form of a pressure equalizing valve and at least one valve is in the form of a differential pressure control valve. In the second chamber of the differential pressure control valve there prevails the fuel pressure upstream of the metering valves and the first chamber of the differential pressure control valve communicates with the second chamber of each pressure equalizing valve.
Fuel injection systems of this type are designed to produce a corresponding variation in the flow passage cross section of the downstream valves in response to the regulated fuel quantity acting on the metering valves and corresponding to the operating conditions of the internal combustion engine; and, also with the aid of as constant a pressure drop as possible at this flow passage cross section, to achieve constant and accurate fuel metering corresponding to the free cross section of the downstream valves irrespective of the pressures upstream and downstream of the metering location.
In the case of known fuel injection systems of this type, the fuel for the individual cylinders of the internal combustion engine is metered in common at various control slots by means of a control edge of a control slide. The metering operation takes place with a pressure difference which is kept constant but which is electromagnetically variable by means of a differential pressure control valve as a function of the engine parameters. The construction costs for such a system are relatively high.